From d600d7a6685546f46fd97dafbec4c8c5b91a7bd2 Mon Sep 17 00:00:00 2001
From: factnn <166481866+factnn@users.noreply.github.com>
Date: Sun, 21 Jun 2026 15:56:43 +0800
Subject: [PATCH] fix: also strip reasoning_content from Mistral messages
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Fixes #30835 — reasoning_content in assistant messages causes
422 extra_forbidden when forwarded to Mistral API.
---
 litellm/llms/mistral/chat/transformation.py                     | 2 ++
 .../llms/mistral/test_mistral_chat_transformation.py            | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/litellm/llms/mistral/chat/transformation.py b/litellm/llms/mistral/chat/transformation.py
index ba44d9f2340..8daddde19de 100644
--- a/litellm/llms/mistral/chat/transformation.py
+++ b/litellm/llms/mistral/chat/transformation.py
@@ -272,6 +272,7 @@ class MistralConfig(OpenAIGPTConfig):
                 m.pop("provider_specific_fields", None)
                 m.pop("thinking_blocks", None)
                 m.pop("cache_control", None)
+                m.pop("reasoning_content", None)
             new_messages.append(m)
 
         if is_async:
@@ -306,6 +307,7 @@ class MistralConfig(OpenAIGPTConfig):
                 m.pop("provider_specific_fields", None)
                 m.pop("thinking_blocks", None)
                 m.pop("cache_control", None)
+                m.pop("reasoning_content", None)
         return messages
 
     def _handle_message_with_file(self, messages: List[AllMessageValues]) -> List[AllMessageValues]:
diff --git a/tests/test_litellm/llms/mistral/test_mistral_chat_transformation.py b/tests/test_litellm/llms/mistral/test_mistral_chat_transformation.py
index 3b54aa18a3c..c0ed90efda0 100644
--- a/tests/test_litellm/llms/mistral/test_mistral_chat_transformation.py
+++ b/tests/test_litellm/llms/mistral/test_mistral_chat_transformation.py
@@ -266,6 +266,7 @@ class TestMistralReasoningSupport:
                     "provider_specific_fields": {"foo": "bar"},
                     "thinking_blocks": [],
                     "cache_control": {"type": "ephemeral"},
+                    "reasoning_content": "some thinking",
                 },
             )
         ]
@@ -278,6 +279,7 @@ class TestMistralReasoningSupport:
         assert "provider_specific_fields" not in msg
         assert "thinking_blocks" not in msg
         assert "cache_control" not in msg
+        assert "reasoning_content" not in msg
 
     def test_transform_request_magistral_with_reasoning(self):
         """Test transform_request method for magistral model with reasoning."""